1. Technical Field
The present invention relates to a method of forming a metal pattern. More specifically, the present invention relates to a method of forming a metal pattern including a plurality of metal layers.
2. Related Art
Wires of ICs and LSICs or liquid crystal displays are generally created by forming a metal film on a substrate and etching the metal film into a predetermined metal pattern using a resist film patterned by a photolithography method. For example, when a gold (Au) wire is formed, a close adhesion layer made of Nichrome (NiCr) is generally placed between the substrate and the Au layer so as to create a close adhesion between the Au layer and the substrate. When a wire formed of a metal pattern including an NiCr layer and an Au layer is formed, the NiCr layer and the Au layer are also etched using a resist film. Often, however, the etching liquid also reaches the side surfaces of the NiCr and Au layer that are not masked by the resist film acting and side etching occurs when the etchant undercuts the resist film. Thus, side etching may reduce the width of the NiCr layer and the Au layer more than the width of the etching mask, causing the side surfaces of the wire to become tapered. In addition, other difficulties arise when the resist film is peeled off from the metal film during the etching process, causing additional incidences of side etching. Thus, it is often difficult to obtain a wire having a desired width using the etching process.
In order to suppress side etching, it has been attempted to improve the etchant itself by adjusting the concentration of the etchant and the like. A technique of controlling an etching speed of gold or similar metal by performing an etching process using as an etchant an aqueous solution containing iodine and a compound (surfactant) having at least one alcoholic hydroxyl group in a side chain thereof has been disclosed (see JP-A-2003-229420 and JP-A-2003-109949). However, these attempts to improve the etchant generally result in poorer etching performance than found with traditional etchants.
Thus it is difficult to obtain a metal pattern having a desired width which includes a plurality of metal layers.